Laser discharge tube

ABSTRACT

Disclosed are devices for causing electrical discharges in gases. The devices are characterized by the fact that the cathode includes sharp edged protuberances.

Elited States Farcy et a1.

[ June 19, 1973 LASER DISCHARGE TUBE Inventors: Jean-Claude Farcy,

Saint-Michel-sur-Orge; Roger Dumanchin, Orsay; Jean Rocca-Serra, Paris,all of France Assignee: Compagnie Generale DElectricite,

Paris, France Filed: Mar. 17, 1971 Appl. No.: 125,037

Foreign Application Priority Data Mar. 23, 1970 France ..33l/94.5 (ireatBritain ..331/94.5

US. Cl. 331/945, 330/43, 313/309,

Int. Cl. H015 3/09, H015 3/02, HOls 3/22 Field of Search 331/945;330/43;

Primary Examiner-Ronald L. Wibert Assistant Examiner-R. J. WebsterAtt0rneySughrue, Rothwell, Mion, Zinn & Macpeak 57 ABSTRACT Disclosedare devices for causing electrical discharges in gases. The devices arecharacterized by the fact that the cathode includes sharp edgedprotuberances.

18 Claims, 8 Drawing Figures l///V7////////// A PATENTED Jun 9 ma SHEET1 BF 2 FIGS LASER DISCHARGE TUBE BACKGROUND OF THE INVENTION Thisinvention relates to gas laser discharge tubes in which the activegaseous medium is at a relatively high pressure. The gas pressure may beequal to or greater than atmospheric pressure.

It is known that if a metallic piece with a pointed end, that is, an endwhose surface has a radius of curvature that is as close to zero aspossible is brought to high electric potential there will be acontraction of the electric field force lines within the vicinity of themetallic piece thus producing very high electric fields. For example,these fields may be on the order of volts/cm. This effect is commonlycalled the point effect.

SUMMARY OF THE INVENTION This invention is intended to create structuresin an electrical discharge tube of a gas laser generator for obtaininghomogeneous discharges, without electric arc, with considerable activevolumes and with high repetition rates through the application ofrelatively low electrical voltages.

This invention concerns a discharge tube for gas laser generatorswhichinclude an anode and a cathode characterized by the fact that at leastone portion of the cathode has at least one protuberance which has asharp end, at least one auxiliary electrical conductor, associated withsaid cathode and arranged in the proximity of said sharp end andseparated therefrom by a solid insulating material.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of thisinvention will appear in the course of the detailed description belowwhile referring to the attached drawings given here by way ofillustration of which:

FIGS. 1 and 2 represent, respectively, a cross section of two variantsof a coaxial discharge tube with multiple axial plates,

FIGS. 3 and 4, respectively, represent a cross section of twovariants'of a coaxial discharge tube with single helicoidal plate,

FIG. 5 represents, in a cross section, a first variant of a dischargedevice with electrodes forming a flat assembly and involving flatstraight and normal plates,

FIG. 6 represents, in cross section, a second variant of a dischargedevice with electrodes forming an essentially plane assembly,

FIG. 7 represents a cross section of a third variant with electrodes,

FIG. 8 represents another variant with electrodes forming a planeassembly in which the protuberances come in the form of transversalrods.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 represents across section of a discharge tube constructed in accordance with oneembodiment of this invention. The discharge device has a coaxialstructure and includes a central conductor 1 which is coupled to apositive potential and an exterior conductor 2 which is coupled tonegative potential. The exterior conductor has, on its inside surface, aseries of thin plates 3, preferably as fine as possible, arrangedaxially and directed toward the central conductor 1.

These thin plates, which for example, can be steel plates, such as razorblades or the like, have an edge that should be as sharp as possible soas to obtain as sharp a point as possible.

According to one embodiment of the invention, auxiliary electricalconductors 5 are arranged in the space bounded by two consecutiveplates. Conductor 5 is separated from the lateral surface of the plates3 and from the inside surface of the conductor 2 by the solid insulatingmaterial 4. This insulating material may enclose the conductor 5 beforeit is put in place between plates 3 or, it may be poured directly intothe space between the plates. This insulating material 4 must of coursehave suitable characteristics to prevent its destruction due to heat,the decomposition products of the gases, contained in the dischargedevice, etc.

Electrical conductors, such as 5, are brought to a potential higher thanthe conductor 2-3. This may be done by electrically connecting conductor5 with conductor 1.

Conductor 5 is preferably placed as close as possible to the edges ofthe two consecutive plates. As we explained earlier, the point effectproduces the tearingaway of electrons, starting the discharge betweenthe negative electrodes (2-3) and the positive electrode 1. Thedistribution of plates 3 creates a very homogeneous discharge, while thefineness of the edges of these plates makes it possible to make adischarge in a gas under a relatively high pressure, with a relativelylow voltage. The addition of conductors 5, which have a positivepotential with respect to the cathode, acts as an auxiliary electrode,promoting the creation of electrons while improving the homogeneity ofthe discharge. The effect of conductors 5 is especially beneficial whenarranged close to the active portion (edge) of plates 3.

FIG. 2 shows a cross section of another possible way of implementing theinvention. This second device is distinguished from the earlier one onlyby the fact that the plates and the auxiliary conductors are arranged onthe surface of the interior conductor 22 of the coaxial structure 21,22.

FIG. 3 shows an axial cross section of a variant of the device accordingto FIG. 1. According to this embodiment, instead of using a plurality ofplates arranged axially, we employ a single helicoidal plate 6, attachedto the inside surface of the outside conductor 32 of the coaxialstructure (31, 32).

In FIG. 4 the plurality of axial plates shown in FIG. 3 is replaced by asingle helicoidal plate 7, attached to central conductor 42 of thecoaxial structure 41, 42. Of course, in the case of FIGS. 3 and 4, theinsulated auxiliary conductor 8 is formed from a single helicoidallyarranged conductor.

FIG. 5 shows another embodiment of the invention. In FIG. 5, electrodes9 and 10 are planar, the sharpedged plates 11 are arranged parallel onthe cathode 9, and auxiliary conductors 12 include an insulation 13arranged essentially co-planar with the edges of plates.

Surfaces 14 can be deposited, for example, with a brush by any othersuitable means and their edges must also be as fine as possible in orderto make up a sharp edge 16 which will produce a large point effect.

Rod is advantageously made of insulating material and will serve as aninsulating envelope for conductor 17 which is given a positive potentialwith respect to the cathode. This may be done, for example, byconnecting conductor 17 to the anode 18. This metallic conductor playsthe same role as conductors 5, 8 and 12 in the preceding figures.

FIG. 7 shows a cross section of another embodiment wherein the negativeelectrode of the cell consists of deposited metallic surfaces 19,arranged on a flat insulating support 20. Associated with this supportis a metallic conductor 61 which, although placed behind surfaces 19, isconnected in the same fashion as the conductors 5, 8, l2 and 17 in thepreceding figures and which plays the same role as these conductors.Conductors 61 may be massive or may be a fine layer of metal.

It is of course understood that surfaces 14 and 19 can be made eitherfrom a pure metal or an alloy and can be made from a metallized paint,the deposit being made here in any known manner so as to obtain sharpedges.

FIG. 8 is a cross section of a device which is a variation of thatillustrated in FIG. 5. In FIG. 8, we fragment the plates by usingseparate rods with sharpened ends. According to this variant, rods 51,kept in place by an insulating piece 52, are connected to the negativeterminal of a high-voltage source, either by individual conductors or bymeans of a metallic plate 23.

In FIG. 8, the auxiliary conductors play a role similar to theconductors 5, 8, l7 and 61 in the preceding figures and are made in theform of a cylinder 24 surrounding each of the rods 51 with theinterposition of an insulating agent 25.

To avoid untimely discharge between rod 51 and conductor 24, the lattersend will preferably be covered with an insulating agent as illustratedby portion 26, shown on the element situated to the right in FIG. 8.

Of course, each laser discharge tube is arranged in a resonant cavity,made up of at least two reflecting mirrors, so that the optical axis ofthis cavity will be either essentially parallel to the anode andessentially at an equal distance between this plane and the planedefined by the ends of the points of the cavity for the plane dischargetubes and will merge with the axis of the central electrode for thetubes with coaxial structure.

What is claimed is:

1. In a gas laser generator including a discharge tube having an anodeand a cathode, the improvement comprising:

a. said cathode including at least one plate, having a sharp bevelededge, and

b. at least one auxiliary electrical conductor arranged adjacent saidsharp edge of said plate, whereby said sharp edged plate and saidauxiliary conductor aids in the creation of a discharge between saidcathode and said anode.

2. The discharge tube of claim 1 further including insulation meansseparating said auxiliary conductor from said cathode and means forcausing said auxiliary conductor to obtain an electric potentialpositive with respect to said cathode.

3. The discharge tube of claim 2 wherein said cathode is cylindrical andcomprises a plurality of said sharp edge plates spaced along thecircumference thereof and a plurality of said auxiliary conductors, onespaced between each successive pair of plates.

4. The discharge tube of claim 3 wherein said sharp edged plates arespaced along the inside circumference of said cathode.

5. The discharge tube of claim 3 wherein said sharp edged plates arespaced along the outside circumference of said cathode.

6. The discharge tube of claim 3 wherein said cathode and anode form acoaxial structure.

7. The discharge tube of claim 2 wherein said cathod and anode are eachof a planar structure, said sharp edge of said plate being arrangedessentially normal to one planar surface of said cathode.

8. The discharge tube of claim 7 further comprising a plurality of saidplates and said auxiliary conductors, each of said auxiliary conductorsbeing spaced between a pair of said plates.

9. The discharge tube of claim 1 wherein said cathode and anode form acoaxial structure said plate are formed by the edge of a singlehelicoidal plate arranged on the surface of said cathode.

10. The discharge tube of claim 9 wherein said auxiliary conductor is ahelical.

11. The discharge tube of claim 1 wherein said auxiliary conductors andsaid plates are plural in number and wherein said auxiliary conductorsare arranged essentially coplanar with said sharp edges of said plates.

12. The discharge tube of claim 2 wherein said auxiliary conductor iscylindrical and said insulating means includes a solid insulatingmaterial disposed around said auxiliary conductor.

13. The discharge tube of claim 1 wherein said auxiliary conductor istubular and surrounds said plate.

14. The discharge tube of claim 2 wherein said insulation means includesa solid insulating material and said cathode is a metallic depositformed on said insulating material which terminates in a sharp taperededge.

15. The discharge tube of claim 14 wherein said solid insulatingmaterial is a tube with an essentially cylindrical cross section.

16. The discharge tube of claim 15 wherein said auxiliary conductor isembedded in said tube shaped insulating material.

17. The discharge tube of claim 14 wherein said insulating material isessentially planar in structure.

18. The discharge tube of claim 17 wherein said auxiliary conductor is ametallic deposit on said planar insulating material on the face oppositethe one on which is deposited said cathode.

1. In a gas laser generator including a discharge tube having an anodeand a cathode, the improvement comprising: a. said cathode including atleast one plate, having a sharp beveled edge, and b. at least oneauxiliary electrical conductor arranged adjacent said sharp edge of saidplate, whereby said sharp edged plate and said auxiliary conductor aidsin the creation of a discharge between said cathode and said anode. 2.The discharge tube of claim 1 further including insulation meansseparating said auxiliary conductor from said cathode and means forcausing said auxiliary conductor to obtain an electric potentialpositive with respect to said cathode.
 3. The discharge tube of claim 2wherein said cathode is cylindrical and comprises a plurality of saidsharp edge plates spaced along the circumference thereof and a pluralityof said auxiliary conductors, one spaced between each successive pair ofplates.
 4. The discharge tube of claim 3 wherein said sharp edged platesare spaced along the inside circumference of said cathode.
 5. Thedischarge tube of claim 3 wherein said sharp edged plates are spacedalong the outside circumference of said cathode.
 6. The discharge tubeof claim 3 wherein said cathode and anode form a coaxial structure. 7.The discharge tube of claim 2 wherein said cathod and anode are each ofa planar structure, said sharp edge of said plate being arrangedessentially normal to one planar surface of said cathode.
 8. Thedischarge tube of claim 7 further comprising a plurality of said platesand said auxiliary conductors, each of said auxiliary conductors beingspaced between a pair of said plates.
 9. The discharge tube of claim 1wherein said cathode and anode form a coaxial structure said plate areformed by the edge of a single helicoidal plate arranged on the surfaceof said cathode.
 10. The discharge tube of claim 9 wherein saidauxiliary conductor is a helical.
 11. The discharge tube of claim 1wherein said auxiliary conductors and said plates are plural in numberand wherein said auxiliary conductors are arranged essentiAlly coplanarwith said sharp edges of said plates.
 12. The discharge tube of claim 2wherein said auxiliary conductor is cylindrical and said insulatingmeans includes a solid insulating material disposed around saidauxiliary conductor.
 13. The discharge tube of claim 1 wherein saidauxiliary conductor is tubular and surrounds said plate.
 14. Thedischarge tube of claim 2 wherein said insulation means includes a solidinsulating material and said cathode is a metallic deposit formed onsaid insulating material which terminates in a sharp tapered edge. 15.The discharge tube of claim 14 wherein said solid insulating material isa tube with an essentially cylindrical cross section.
 16. The dischargetube of claim 15 wherein said auxiliary conductor is embedded in saidtube shaped insulating material.
 17. The discharge tube of claim 14wherein said insulating material is essentially planar in structure. 18.The discharge tube of claim 17 wherein said auxiliary conductor is ametallic deposit on said planar insulating material on the face oppositethe one on which is deposited said cathode.